Steadily growing worldwide production of phosphate-based agricultural fertilizers such as diammonium phosphate, triple superphosate and superphosphoric acid, and of animal feed supplement such as dicalcium phosphate has resulted in ever increasing consumption of the principal raw material, phosphate rock, used for the manufacture of these end products.
The most desirable grades of phosphate rock, those with the highest BPL, are now scarce. BPL is the short name used in the art for bone phosphate of lime, or tri-calcium phosphate. Phosphate rock with a BPL concentration of 75 or higher were available and used some years ago for industrial manufacture of the end products referred to above. Today the BPL of the rock used is down to 68 and lower. In the future it is expected that the industry will have to use rock with BPL's as low as 64, and lower.
There exists large reserves of phosphate rock of less than 64 BPL. Expressed as phosphorus pentoxide (P.sub.2 O.sub.5) equivalent (the customary measure of phosphorus content used in the fertilizer industry) this would be 29.3% P.sub.2 O.sub.5. It generally is considered at the present time to be uneconomical to use such low BPL rock industrially. For the manufacture by wet-phosphoric acid processes of the end products mentioned above, phosphate rock of less than 64 BPL (29.3% P.sub.2 O.sub.5) is not economical.
Thus there exists a need which is expected to increase in the future for a new low cost, economical and industrially acceptable method for upgrading or beneficiating phosphate rock of low BPL.
There also exists a need for a new low cost, economical method which is industrially acceptable for upgrading or beneficiating phosphatic rock, slime, or tailings. Nearly one-third of all the phosphate rock mined and washed ends up as slime or tailings, which have phosphatic values (BPL) so low that they cannot be used economically for the manufacture of fertilizer or animal feed products. If the BPL concentration of these slimes or tailings can be increased sufficiently by a low cost commercially practicable method, then such slime or tailings could be used for the manufacture of fertilizer and animal feed products rather than being discarded as waste.